Display device with micro cover layer and manufacturing method for the same

ABSTRACT

There is provided a flexible display having a plurality of innovations configured to allow bending of a portion or portions to reduce apparent border size and/or utilize the side surface of an assembled flexible display.

BACKGROUND

1. Technical Field

This relates generally to electronic devices, and more particularly, toelectronic devices with a display.

2. Description of the Related Art

Electronic devices often include displays. For example, cellulartelephones and portable computers include displays for presentinginformation to a user. Components for the electronic device, includingbut not limited to a display, may be mounted in the housing made ofplastic or metal.

An assembled display may include a display panel and a number ofcomponents for providing a variety of functionalities. For instance, oneor more display driving circuits for controlling the display panel maybe included in a display assembly. Examples of the driving circuitsinclude gate drivers, emission (source) drivers, power (VDD) routing,electrostatic discharge (ESD) circuits, multiplex (mux) circuits, datasignal lines, cathode contacts, and other functional elements. There maybe a number of peripheral circuits included in the display assembly forproviding various kinds of extra functions, such as touch sense orfingerprint identification functionalities.

Some of the components may be disposed on the display panel itself,often in the areas peripheral to the display area, which is referred inthe present disclosure as the non-display area and/or the inactive area.When such components are provided in the display panel, they populate asignificant portion of the display panel. Large inactive area tends tomake the display panel bulky, making it difficult to incorporate it intothe housing of electronic devices. Large inactive area may also requirea significant portion of the display panel to be covered by overly largemasking (e.g., bezel, borders, covering material), leading tounappealing device aesthetics.

Size and weight are of the critical importance in designing modernelectronic devices. Also, a high ratio of the active area size comparedto that of inactive area, which is sometimes referred to as the screento bezel ratio, is one of the most desired feature. There is a limit asto how much reduction in the size of the inactive area for higherscreen-to-bezel ratio can be realized from mere use of a separateflexible printed circuit (FPC) for connecting components to the displaypanel. Space requirement for reliably attaching signal cables and to fanout wires along the edges of the display panel still needs to bedisposed in the inactive area of the display panel.

It will be highly desirable to bend the base substrate where the activewith the pixels and the inactive area are formed thereon. This wouldtruly minimize the inactive area of the display panel that needs to behidden under the masking or the device housing. Not only does thebending of the base substrate will minimize the inactive area size needto be hidden from view, but it will also open possibility to various newdisplay device designs.

However, there are various new challenges that need to be solved inproviding such flexible displays. The components formed directly on thebase substrate along with the display pixels tend to have tremendouslysmall dimension with unforgiving margin of errors. Further, thesecomponents need to be formed on extremely thin sheet to provideflexibility, making those components extremely fragile to variousmechanical and environmental stresses instigated during the manufactureand/or in the use of the displays.

Further complication arises from the fact that the components fabricateddirectly on the base substrate with the display pixels are often closelylinked to the operation of those pixels. If care is not taken, themechanical stresses from bending of the flexible display can negativelyaffect the reliability or even result in complete component failure.Even a micro-scale defect in the component thereof can have devastatingeffects on the performance and/or reliability of the display pixelsamounting to scrap the entire display panel without an option to repair.

For instance, a few micrometer scale cracks in the electric wires cancause various abnormal display issues and may even pixels in severalrows or sections of the display panel not to be activated at all. Assuch, various special parameters must be taken in consideration whendesigning electrical wiring schemes to be fabricated on the flexiblebase substrate along with the display pixels. Simply increasing thebending radius may make it difficult to garner any significant benefitsin flexing the base substrate of the display panel. It would thereforebe desirable to provide a flexible display that can operate reliablyeven under the bending stresses from extreme bending radius.

SUMMARY

An aspect of the present disclosure is related to a flexible display,which includes configurations for wire traces to withstand bendingstress for reliable operation of the flexible display.

In one embodiment, a display apparatus includes a base layer with a bendallowance section between a first portion and a second portion. Thefirst portion of the display apparatus includes an active area where aplurality of organic light-emitting diode (OLED) elements is disposed.The display apparatus further includes an encapsulation over the OLEDelements. The encapsulation may be provided in a form of a film. Aprinted circuit film may be provided in the second portion of thedisplay apparatus. The printed circuit film may be a driving circuit foroperating the OLED elements. The display apparatus further includes amicro-coating layer, which is disposed over the bend allowance sectionof the display apparatus.

In some embodiments, the display apparatus includes a plurality of wiretraces routed between the first portion and the second portion of thebase layer. In this case, the plurality of conductive line traces in thebend allowance section is covered by the micro-coating layer.

In some embodiments, the micro-coating layer can be disposed over atleast a part of the encapsulation. More specifically, the displayapparatus may include a polarization layer on the encapsulation. Theedge of the polarization layer is shifted towards the active area fromthe edge of the encapsulation. This leaves a part of the upper surfaceof the encapsulation open, so that the micro-coating layer can cover atleast part of the upper surface of the encapsulation exposed between anedge of polarization layer and an edge of the encapsulation. Theadditional contact area between the micro-coating layer and the surfaceof the encapsulation can provide stronger bonding between the two. Theenhanced sealing between the encapsulation and the micro-coating layercan hinder the moisture and other foreign materials from corroding thewire traces under the micro-coating layer.

In some embodiments, the micro-coating layer covering the upper surfaceof the encapsulation may include a part where it is spaced apart fromthe sidewall of the polarization layer. In some embodiments, themicro-coating layer covering the upper surface of the encapsulation mayinclude a part where it is in contact with the sidewall of thepolarization layer.

In some embodiments, the display apparatus includes the part where themicro-coating layer is spaced apart from the sidewall of thepolarization layer as well as the part where the micro-coating layer isin contact with the sidewall of the polarization layer. The part wherethe micro-coating layer and the polarization layer contact each othermay be located towards the notched edge of the flexible display. Thecontact between the micro-coating layer and the polarization layer mayallow to hold the printed circuit film in position and reduce possiblecrack generation from unwanted movement of the printed circuit film.

In some embodiments, the micro-coating layer may have higher profiletowards the encapsulation than the micro-coating layer in towards theprinted circuit film. The lower profile of the micro-coating layertowards the printed circuit film can be advantageous for reducingunwanted space at the rear side of the display apparatus after bending.

The thickness of the micro-coating layer may be substantially uniformbetween the encapsulation and the printed circuit film. In particular,the difference in thicknesses of the micro-coating layer between thethickest micro-coating layer and the thinnest micro-coating layer inthis region may be less than 50 um.

The thickness of the micro-coating layer may be adjust the neutral planeof the display apparatus at the bend portion. The added thickness at thebend portion of the display apparatus by the micro-coating layer canshift the neutral plane towards the plane of the wire traces so thatreduced amount of bending stress is applied to the wire traces.

In another aspect, a method of manufacturing a flexible display isprovided. In one embodiment, a buffer layer is formed over the baselayer. On top of the buffer layer, conductive line traces with a strainreducing pattern. After the conductive line trace is formed on thebuffer layer, the base layer is chamfered to create a notched inactivearea. The notched inactive area can include a bend allowance section.Since cracks can initiate and propagate from the chamfered or scribededge of the flexible display, the buffer layer is etched to expose thebase layer along strain reducing pattern of the conductive line traceand along the notched line. Although removing the inorganic layer nearthe notched line can inhibit crack initiation from bending stress it canmake the conductive lines vulnerable from moistures and other foreignmaterials. Accordingly, a micro-coating layer is dispensed in thenotched inactive area. The micro-coating layer may be dispensed in aresinous form. The micro-coating layer is then cured by irradiation oflight.

In some embodiments, the micro-coating layer can be dispensed by using ajetting valve. The dispensing speed from the jetting valve may beadjusted during the dispensing process for accurate control of thethickness and the spread size of the micro-coating layer at the targetedsurface. Further, additional number of jetting values may be used toreduce the dispense time and limit the amount of spread before themicro-coating layer is cured through UV irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate schematic view of an exemplary flexible displaydevice according to embodiments of the present disclosure.

FIGS. 2A-2B illustrate schematic view of an exemplary flexible displaydevice according to embodiments of the present disclosure.

FIG. 3 illustrates schematic plane view and correspondingcross-sectional view of bending pattern, which may be employed inembodiments of the present disclosure.

FIGS. 4A-4B illustrate schematic view of an exemplary multi-layeredconductive lines usable in a flexible display device according toembodiments of the present disclosure.

FIGS. 5A-5B illustrate schematic view of an exemplary configuration ofmulti-layered conductive lines and insulation layers according toembodiments of the present disclosure.

FIG. 6A illustrates schematic view of an exemplary configuration ofrecessed channel and crack deflection metal/insulation trace accordingto embodiments of the present disclosure.

FIGS. 6B-6C illustrate schematic view of an exemplary configurationbuffer etched area provided in between the notched line and the bendallowance section.

FIG. 7 is a schematic view of single line wire trace design usable forflexible displays according to an embodiment of the present disclosure.

FIGS. 8A-8D illustrate schematic view of an exemplary wire traces havinga plurality of sub-traces that split and merge at a certain intervalaccording to embodiments of the present disclosure.

FIGS. 9A-9B illustrate schematic view of an exemplary wire tracescrossing recessed area of the flexible display according to embodimentsof the present disclosure.

FIGS. 10A-C illustrate schematic views of the flexible display providedwith a micro-coating layer according to embodiments of the presentdisclosure.

FIGS. 11A-B illustrate schematic views of embodiments of the flexibledisplay in a bent state, which are provided with a micro-coating layeraccording to embodiments of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1A-1C illustrate exemplary flexible display 100 which may beincorporated in electronic devices. Referring to FIG. 1A, the flexibledisplay 100 includes at least one active area (i.e., display area), inwhich an array of display pixels are formed therein. One or moreinactive areas may be provided at the periphery of the active area. Thatis, the inactive area may be adjacent to one or more sides of the activearea. In FIG. 1A, the inactive area surrounds a rectangular shape activearea. However, it should be appreciated that the shapes of the activearea and the arrangement of the inactive area adjacent to the activearea are not particularly limited as the exemplary flexible display 100illustrated in FIG. 1A. The active area and the inactive area may be inany shape suitable to the design of the electronic device employing theflexible display 100. Non-limiting examples of the active area shapes inthe flexible display 100 include a pentagonal shape, a hexagonal shape,a circular shape, an oval shape, and more.

Each pixel in the active area may be associated with a pixel circuit,which includes at least one switching thin-film transistor (TFT) and atleast one driving TFT. Each pixel circuit may be electrically connectedto a gate line and a data line to communicate with the driving circuits,such as a gate driver and a data driver, which are positioned in theinactive area of the flexible display 100.

For example, one or more driving circuits may be implemented with TFTsfabricated in the inactive area as depicted in FIG. 1A. Such gatedrivers may be referred to as a gate-in-panel (GIP). Also, some of thecomponents, such as data drive-IC, may be mounted on a separate printedcircuit and coupled to a connection interface (Pads/Bumps) disposed inthe inactive area using a printed circuit film such as flexible printedcircuit board (FPCB), chip-on-film (COF), tape-carrier-package (TCP) orany other suitable technologies. As will be described in further detailbelow, the inactive area with the connection interface can be bent awayfrom the central portion so that the printed circuit film, such as theCOF, FPCB and the like, is positioned at the rear side of the flexibledisplay 100 to reduce the size of the inactive area to be hidden by abezel.

The flexible display 100 may include various additional components forgenerating a variety of signals or otherwise operating the pixels in theactive area. For example, an inverter circuit, a multiplexer, an electrostatic discharge (ESD) circuit and the like may be placed in theinactive area of the flexible display 100.

The flexible display 100 may also include components associated withfunctionalities other than for operating the pixels of the flexibledisplay 100. For instance, the flexible display 100 may includecomponents for providing a touch sensing functionality, a userauthentication functionality (e.g., finger print scan), a multi-levelpressure sensing functionality, a tactile feedback functionality and/orvarious other functionalities for the electronic device employing theflexible display 100. These components can be placed in the inactivearea or provided on a separate printed circuit that is connected to theconnection interface of the flexible display 100.

In some embodiments, the backplane of the flexible display 100 can beimplemented with TFTs using low-temperature poly-silicon (LTPS)semiconductor layer as its active layer. Accordingly, the pixel circuitand the driving circuits (e.g., GIP) are implemented with NMOS LTPSTFTs. In some other embodiments, the backplane of the flexible display100 may be implemented with a combination of N-Type LTPS TFTs and P-TypeLTPS TFTs. For instance, the flexible display 100 may be provided with aCMOS GIP, implemented by using both the N-Type LTPS TFTs and P-Type LTPSTFTs.

Further, in some embodiments, the flexible display 100 may employmultiple kinds of TFTs to implement the driving circuits in the inactivearea and/or the pixel circuits in the active. That is, a combination ofan oxide semiconductor TFT and an LTPS TFT may be used to implement thebackplane of the flexible display 100. In the backplane, the type ofTFTs may be selected according to the operating conditions and/orrequirements of the TFTs within the corresponding circuit.

Low-temperature-poly-silicon (LTPS) TFTs generally exhibit excellentcarrier mobility even at a small profile, making them suitable forimplementing condensed driving circuits. The excellent carrier mobilityof the LTPS TFT makes it an ideal for components requiring a fast speedoperation. Despite the aforementioned advantages, initial thresholdvoltages may vary among the LTPS TFTs due to the grain boundary of thepoly-crystallized silicon semiconductor layer.

On the other hand, a TFT employing an oxide material based semiconductorlayer such as an indium-gallium-zinc-oxide (IGZO) semiconductor layer(referred hereinafter as “the oxide TFT”), is different from the LTPSTFT in many respects. Although the oxide TFT has a lower mobility thanthe LTPS TFT, the oxide TFT is generally more advantageous than the LTPSTFT in terms of reducing the leakage current during its off state. Inother words, the oxide TFT generally exhibits a higher voltage-holdingratio (VHR) than that of the LTPS TFT. The higher VHR of the oxide TFTcan be of a great advantage for driving the pixels at a reduced framerate when a high frame rate driving of the pixels is not needed.

In some embodiments, the flexible display 100 may be provided with afeature in which the pixels of the entire active area or selectiveportion of the active area are driven at a reduced frame rate under aspecific condition. In way of an example, the pixels can be refreshed ata reduced refresh rate depending on the content displayed from theflexible display 100. Also, part of the active area displaying a stillimage data (e.g., user interface, text) may be refreshed at a lower ratethan other part of the active area displaying rapidly changing imagedata (e.g., movie). The pixels driven at a reduced refresh rate may havean increased blank period, in which the data signal is not provided tothe pixels. This would minimize the power wasted from providing thepixels with the same image data. In such embodiments, oxide TFTs can beused for some of the TFTs implementing the pixel circuits and/or thedriving circuits of the flexible display 100 to minimize the leakagecurrent during the blank period. By reducing the current leakage fromthe pixel circuits and/or the driving circuits, more stable level ofbrightness can be achieved from the pixels even when they are refreshedat a reduced rate.

In terms of stability, oxide TFTs do not suffer from thetransistor-to-transistor initial threshold voltage variation issue asmuch as the LTPS TFTs. Such property can be of a great advantage if theflexible display 100 is large. On the other hand, the LTPS TFT may bebetter than the oxide TFT in terms of the positive bias temperaturestress (PBTS) and the negative bias temperature stress (NBTIS), whichmay cause unwanted threshold voltage shift during the use of theflexible display 100.

Considering the pros and cons of LTPS TFT and oxide TFT, someembodiments of the flexible display 100 disclosed herein may employ acombination of the LTPS TFT and the oxide TFT. In particular, someembodiments of the flexible display 100 can employ LTPS TFTs toimplement the driving circuits (e.g., GIP) in the inactive area andemploy oxide TFTs to implement the pixel circuits in the active area.Due to the excellent carrier mobility of the LTPS TFT, driving circuitsimplemented with LTPS TFTs may operate at a faster speed than thedriving circuits implemented with the oxide TFTs. In addition, morecondensed driving circuits can be provided with the LTPS TFT, whichreduces the size of the inactive area in the flexible display 100.

With the excellent voltage holding ratio of the oxide TFTs used in thepixel circuits, leakage from the pixels can be reduced. This alsoenables to refresh pixels in a selective portion of the active area orto drive pixels at a reduced frame rate under a predetermined condition(e.g., when displaying still images) while minimizing display defectscaused by the leakage current.

In some embodiments, the driving circuits in the inactive area of theflexible display 100 may be implemented with a combination of N-TypeLTPS TFTs and P-Type LTPS TFTs while the pixel circuits are implementedwith oxide TFTs. For instance, N-Type LTPS TFTs and P-Type LTPS TFTs canbe used to implement CMOS gate driver (e.g., CMOS GIP) whereas oxideTFTs are employed in at least some part of the pixel circuits. Unlikethe GIP formed entirely of either the P-type or N-type LTPS TFTs, thegate out node from the CMOS gate driver can be controlled by DC signals,and this allows for more stable control of the gate out node during theblank period.

It should be noted that the CMOS gate driver can be implemented by usinga combination of LTPS TFTs and oxide TFTs. Likewise, in someembodiments, the pixel circuits in the active area can be implemented byusing both the LTPS TFTs and the oxide TFTs. When employing both kindsof TFTs in the pixel circuit and/or the driving circuit, the LTPS TFTcan be used for TFTs of the circuit, which are subjected to extendedperiod of bias stress (e.g., PBTS, NBTIS). In addition, the TFTs in acircuit, which are connected to a storage capacitor, can be formed ofthe oxide TFT to minimize leakage therefrom.

Parts of the flexible display 100 may be defined by a central portionand a bend portion. In reference to a bend line BL, the part of theflexible display 100 that remains substantially flat is referred to asthe central portion or the substantially flat portion, whereas the otherpart of the flexible display 100 at the other side of the bend line BLis referred to as the bend portion. It should be noted that the centralportion of the flexible display 100 needs not be perfectly flat. Whilethe central portion of the flexible display 100 is relatively more flatthan the bend portion, the central portion can be curved-in orcurved-out as depicted in FIG. 1B. In other words, one or more bendportions exist next to the convex or concave central portion, and bentinwardly or outwardly along the bend line at a bend angle around a bendaxis. Within a bend portion, the part that has a curvature in aninclination angle or in a declination angle from the substantially flatportion may be specified as the bend allowance section of the bendportion.

Multiple parts of the flexible display 100 can be bent along the bendline BL. The bend line BL in the flexible display 100 may extendhorizontally (e.g., X-axis shown in FIG. 1A), vertically (e.g., Y-axisshown in FIG. 1A) or even diagonally. Accordingly, the flexible display100 can be bent in any combination of horizontal, vertical and/ordiagonal directions based on the desired design of the flexible display100.

One or more edges of the flexible display 100 can be bent away from theplane of the central portion along the bend line BL. Although the bendline BL is depicted as being located near the edges of the flexibledisplay 100, it should be noted that the bend lines BL can extend acrossthe central portion or extend diagonally at one or more corners of theflexible display 100. Such configurations would allow the flexibledisplay 100 to provide a foldable display or a double-sided displayhaving display pixels on both outer sides of a folded display.

FIG. 1C is a simplified cross-sectional view of an exemplary flexibledisplay 100 in a bent state. As illustrated in FIG. 1C, the centralportion of the flexible display 100 may be substantially flat, and oneor more bend portions may be bent away from the tangent vector of thecurvature at a certain bend angle and a bend radius around the bendingaxis. The size of each bend portion that is bent away from the centralportion needs not be the same. That is, the length of the base layer 106from the bend line BL to the outer edge of the base layer 106 at eachbend portion can be different from other bend portions. Also, the bendangle around the bend axis and the bend radius from the bend axis canvary between the bend portions.

In the example shown in FIG. 1C, one of the bend portion (right side)has the bend angle θ of 90°, and the bend portion includes asubstantially flat section. The bend portion can be bent at a largerbend angle θ, such that at least some part of the bend portion comesunderneath the plane of the central portion of the flexible display 100as one of the bend portion (left side). Also, a bend portion can be bentat a bend angle θ that is less than 90°.

In some embodiments, the radius of curvatures (i.e., bend radius) forthe bend portions in the flexible display 100 may be between about 0.1mm to about 10 mm, more preferably between about 0.1 mm to about 5 mm,more preferably between about 0.1 mm to about 1 mm, more preferablybetween about 0.1 mm to about 0.5 mm. The lowest bend radius of the bendportion of the flexible display 100 may be less than 0.5 mm.

As shown in FIG. 1C, an organic light-emitting diode (OLED) elementlayer 102 is disposed on the base layer 106, and an encapsulation 104 isdisposed on the organic light-emitting diode (OLED) element layer 102.The flexible display 100 also includes a support member 116, which maybe referred to as a “mandrel.” The support member 116 has an elongatedbody portion and a rounded end portion. The base layer 106 and thesupport member 116 are arranged so that that the rounded end portion ofthe support member 116 is positioned in the bend portion of the baselayer 106. The rounded end portion of the support member 116 providessupport for the base layer 106 at the bend portion. A part of the baselayer 106 may come around the rounded end portion of the support member116 and be positioned at the underside the support member 116 asdepicted in FIG. 1C. In this way, the circuits mounted on thechip-on-flex (COF) cable and/or the printed circuit board (PCB) can beplaced at the rear of the flexible display 100.

The flexible display 100 includes one or more support layers 108 forproviding rigidity at the selective portion of the flexible display 100.The support layer 108 is attached on the inner surface of the base layer106, which is the opposite from the surface having the OLED elementlayer 102 disposed thereon. Increase in the rigidity at selective partsof the flexible display 100 may help in ensuring the accurateconfiguration and placement of the components of the flexible display100.

The base layer 106 and the support layer 108 may each be made of a thinplastic film formed from polyimide, polyethylene naphthalate (PEN),polyethylene terephthalate (PET), other suitable polymers, a combinationof these polymers, etc. However, the support layer 108 should be morerigid than the base layer 106. Other suitable materials that may be usedto form the base layer 106 and the support layer 108 include, a thinglass, a metal foil covered with a dielectric material, a multi-layeredpolymer stack and a polymer composite film comprising a polymer materialcombined with nanoparticles or micro-particles dispersed therein, etc.

Excessively high thickness of the base layer 106 makes it difficult tobe bent at an extremely small bending radius desired at some bendportion of the flexible display 100. Excessively high thickness of thebase layer 106 may also increase the mechanical stress to the componentsdisposed thereon on the base layer 106. As such, the thickness of thebase layer 106 may depend on the bend radius at the bend portion of thebase layer 106. On the other hand, the base layer 106 with a thicknessbelow a certain level may not be strong enough to reliably supportvarious components disposed thereon.

Accordingly, the base layer 106 may have a thickness in a range of aboutfrom 5 μm to about 50 μm, more preferably in a range of about 5 μm toabout 30 μm, and more preferably in a range of about 5 μm to about 16μm. The support layer 108 may have a thickness from about 100 μm toabout 125 μm, from about 50 μm to about 150 μm, from about 75 μm to 200μm, less than 150 μm, or more than 100 μm. In one suitable exemplaryconfiguration, the base layer 106 is formed from a layer of polyimidewith a thickness of about 10 μm and the support layer 108 is formed frompolyethylene terephthalate (PET) with a thickness of about 100 μm toabout 125 μm.

The base layer 106 may be a transparent layer. Part of the flexibledisplay 100 may be exposed to external light passing through the baselayer 106. Some of the components or materials used in fabricating thecomponents disposed on the base layer 106 may undergo undesirable statechanges due to the light exposure during the manufacturing of theflexible display 100. Some parts of the flexible display 100 may be moreheavily exposed to the external light than others, and this can lead toa display non-uniformity (e.g., mura, shadow defects, etc.). To minimizesuch problems, the base layer 106 and/or the support layer 108 mayinclude one or more materials capable of reducing the amount of externallight passing through in some embodiments of the flexible display 100.

In way of an example, the light blocking material, for instance chloridemodified carbon black, may be mixed in the constituent material of thebase layer 106 (e.g., polyimide) so that the base layer 106 can providesa light blocking functionality. In this way, the base layer 106 mayformed of polyimide with a shade. Such a shaded base layer 106 can alsoimprove the visibility of the image content displayed on the flexibledisplay 100 by reducing the reflection of the external light coming infrom the front side of the flexible display 100.

Instead of the base layer 106, the support layer 108 may include a lightblocking material to reduce the amount of light coming in from the rearside (i.e., the support layer 108 attached side) of the flexible display100. The constituent material of the support layer 108 may be mixed withone or more light blocking materials in the similar fashion as describedabove with the base layer 106. Further, both the base layer 106 and thesupport layer 108 can include one or more light blocking materials.Here, the light blocking materials used in the base layer 106 and thesupport layer 108 need not be the same.

While making the base layer 106 and the support layer 108 to block theunwanted external light may improve display uniformity and reducereflection as described above, it can create a number of difficultiesduring manufacturing of the flexible display 100. When the base layer106 and the support layer 108 are non-transmittable to an excessiverange of wavelengths of light, recognizing the alignment marks on theselayers during their alignment process may not be easy. In particular,accurate positioning of the components on the base layer 106 or thealignment during bending of the flexible display 100 can becomedifficult, as the positioning of the layers may need to be determined bycomparing the outer edges of the overlapping portions of the layer(s).Further, checking for unwanted debris or other foreign materials in theflexible display 100 can be problematic if the base layer 106 and/or thesupport layer 108 blocks the excessive range(s) of light spectrum (i.e.,wavelengths in the visible, the ultraviolet and the infrared spectrum).

Accordingly, in some embodiments, the light blocking material, which maybe included in the base layer 106 and/or the support layer 108 isconfigured to pass the light of certain polarization and/or the lightwithin specific wavelength ranges usable in one or more manufacturingand/or testing processes of the flexible display 100. In way of anexample, the support layer 108 may pass the light used in the qualitycheck, alignment processes (e.g., UV, IR spectrum light) during themanufacturing the flexible display 100 but filter the light in thevisible light wavelength range. The limited range of wavelengths canhelp reduce the display non-uniformity problem, which may be caused bythe shadows generated by the printed circuit film attached to base layer106, especially if the base layer 106 includes the light blockingmaterial as described above.

It should be noted that the base layer 106 and the support layer 108 canwork together in blocking and passing specific types of light. Forinstance, the support layer 108 can change the polarization of light,such that the light will not be passable through the base layer 106.This way, certain type of light can penetrate through the support layer108 for various purposes during manufacturing of the flexible display100, but unable to penetrate through the base layer 106 to causeundesired effects to the components disposed on the opposite side of thebase layer 106.

As shown in FIG. 1B, the flexible display 100 may also include apolarization layer 110 for controlling the display characteristics(e.g., external light reflection, color accuracy, luminance, etc.) ofthe flexible display 100. A cover layer 114, which may be a glass layer,may be used to protect the flexible display 100. Electrodes for sensingtouch input from a user may be formed on an interior surface of a coverlayer 114 and/or at least one surface of the polarization layer 110.

The flexible display 100 may further include a separate layer thatincludes the touch sensor electrodes and/or other components associatedwith sensing of touch input (referred hereinafter as touch-sensor layer112). The touch sensor electrodes (e.g., touch driving/sensingelectrodes) may be formed from transparent conductive material such asindium tin oxide, carbon based materials like graphene or carbonnanotube, a conductive polymer, a hybrid material made of mixture ofvarious conductive and non-conductive materials. Also, metal mesh (e.g.,aluminum mesh, silver mesh, etc.) can also be used as the touch sensorelectrodes.

The touch sensor layer 112 may include a layer formed of one or moredeformable dielectric materials. One or more electrodes may beinterfaced with or positioned near the touch sensor layer 112, andloaded with one or more signals to facilitate measuring electricalchanges on one or more of the electrodes upon deformation of the touchsensor layer 112. The measurement may be analyzed to assess the amountof pressure at a plurality of discrete levels and/or ranges of levels onthe flexible display 100.

In some embodiments, the touch sensor electrodes can be utilized inidentifying the location of the user inputs as well as assessing thepressure of the user input. Identifying the location of touch input andmeasuring of the pressure of the touch input on the flexible display 100may be achieved by measuring changes in capacitance from the touchsensor electrodes on one side of the touch sensor layer 112. Also,measuring the amount of pressure may utilize at least one electrodeother than the touch sensor electrodes to measure at least one othersignal, which may be obtained simultaneously with the touch signal fromthe touch sensor electrodes or obtained at a different timing.

The deformable material included in the touch sensor layer 112 may be anelectro-active material, which the amplitude and/or the frequency of thedeformation is controlled by an electrical signal and/or electricalfield. The examples of such deformable materials include piezo ceramic,electro-active-polymer (EAP) and the like. Accordingly, the touch sensorelectrodes and/or separately provided electrode can activate thedeformable material to bend the flexible display 100 to desireddirections. In addition, such electro-active materials can be activatedto vibrate at desired frequencies, thereby providing tactile and/ortexture feedback on the flexible display 100. It should be appreciatedthat the flexible display 100 may employ a plurality of electro-activematerial layers so that bending and vibration of the flexible display100 can be provided simultaneously or at a different timing. Such acombination can be used in creating sound waves from the flexibledisplay 100.

As mentioned above, bending the inactive area allows to minimize or toeliminate the inactive area to be seen from the front side of theassembled flexible display 100. Part of the inactive area that remainsvisible from the front side can be covered with a bezel. The bezel maybe formed, for example, from a stand-alone bezel structure that ismounted to the cover layer 114, a housing or other suitable componentsof the flexible display 100. The inactive area remaining visible fromthe front side may also be hidden under an opaque masking layer, such asblack ink (e.g., a polymer filled with carbon black) or a layer ofopaque metal. Such an opaque masking layer may be provided on a portionof the layers included in the flexible display 100, such as the touchsensor layer 112, the polarization layer 110, the cover layer 114, andother suitable layers.

Referring back to FIG. 1A, the bend portion of the flexible display 100may include an active area capable of displaying image from the bendportion, which is referred herein after as the secondary active area.That is, the bend line BL can be positioned in the active area so thatat least some display pixels of the active area is included in the bendportion of the flexible display 100. In this case, the matrix of pixelsin the secondary active area of the bend portion may be continuouslyextended from the matrix of the pixels in the active area of the centralportion as depicted in FIG. 2A. Alternatively, the secondary active areawithin the bend portion and the active area within the central portionof the flexible display 100 may be separated apart from each other bythe bend allowance section as depicted in FIG. 2B.

The secondary active area in the bend portion may serve as a secondarydisplay area in the flexible display 100. The size of the secondaryactive area is not particularly limited. The size of the secondaryactive area may depend on its functionality within the electronicdevice. For instance, the secondary active area may be used to provideimages and/or texts such a graphical user interface, buttons, textmessages, and the like. In some cases, the secondary active area may beused to provide light of various colors for various purposes (e.g.,status indication light), and thus, the size of the secondary activearea need not be as large as the active area in the central portion ofthe flexible display 100.

The pixels in the secondary active area and the pixels in the centralactive area may be addressed by the driving circuits (e.g., gate driver,data driver, etc.) as if they are in a single matrix. In this case, thepixels of the central active area and the pixels of the secondary activearea may be operated by the same set of driving circuits. In way ofexample, the N^(th) row pixels of the central active area and the N^(th)row pixels of the secondary active area may be configured to receive thegate signal from the same gate driver. As shown in FIG. 2B, the part ofthe gate line crossing over the bend allowance section (i.e., bendallowance region) or a bridge for connecting the gate lines of the twoactive areas may have a bend stress reduction design, which will bedescribed in further detail below.

Depending on the functionality of the secondary active area, the pixelsof the secondary active area can be driven discretely from the pixels inthe central active area. That is, the pixels of the secondary activearea may be recognized by the display driving circuits as being anindependent matrix of pixels separate from the matrix of pixels in thecentral active area. In such cases, the pixels of the central activearea and the pixels of the secondary active area may receive signalsfrom at least one discrete driving circuit from the driving circuitsemployed by the central active area.

Components of the flexible display 100 may make it difficult to bend theflexible display 100 along the bend line BL. Some of the elements, suchas the support layer 108, the touch sensor layer 112, the polarizationlayer 110 and the like, may add too much rigidity to the flexibledisplay 100. Also, the thickness of such elements shifts the neutralplane of the flexible display 100 and thus some of the components may besubject to greater bending stresses than other components.

To facilitate easier bending and to enhance the reliability of theflexible display 100, the configuration of components in the bendportion of the flexible display 100 differs from the substantially flatportion of the flexible display 100. Some of the components existing inthe substantially flat portion may not be disposed in the bend portionsof the flexible display 100, or may be provided in a differentthickness. The bend portion may free of the support layer 108, thepolarization layer 110, the touch sensor layer 114, a color filter layerand/or other components that may hinder bending of the flexible display100. Such components may not be needed in the bend portion if the bendportion is to be hidden from the view or otherwise inaccessible to theusers of the flexible display 100.

Even if the secondary active area is in the bend portion for providinginformation to users, the secondary active area may not require some ofthese components depending on the usage and/or the type of informationprovided by the secondary active area. For example, the polarizationlayer 110 and/or color filter layer may not be needed in the bendportion when the secondary active area is used for simply emittingcolored light, displaying texts or simple graphical user interfaces in acontrast color combination (e.g., black colored texts or icons in whitebackground). Also, the bend portion of the flexible display 100 may befree of the touch sensor layer 114 if such functionality is not neededin the bend portion. If desired, the bend portion may be provided with atouch sensor layer 112 and/or the layer of electro-active material eventhough the secondary active area for displaying information is notprovided in the bend portion.

Since the bend allowance section is most heavily affected by the bendstress, various bend stress-reducing features are applied to thecomponents on the base layer 106 of the bend allowance section. To thisend, some of the elements in the central portion may not be formed in atleast some part of the bend portion. The separation between thecomponents in the central portion and the bend portion may be created byselectively removing the elements at the bend allowance section of theflexible display 100 such that the bend allowance section is free of therespective elements.

As depicted in FIGS. 2A and 2B, the support layer 108A in the centralportion and the support layer 108B in the bend portion can be separatedfrom each other by the absence of the support layer 108 under the baselayer 106 at the bend allowance section. Instead of using the supportlayer 108 attached to the base layer 106, the rounded end portion of thesupport member 116 can be positioned underside of the base layer 106 atthe bend allowance section as described above. Various other components,for example the polarization layer 110 and the touch sensor layer 114and more, may also be absent from the bend allowance section of theflexible display 100. The removal of the elements may be done bycutting, wet etching, dry etching, scribing and breaking, or othersuitable material removal methods. Rather than cutting or otherwiseremoving an element, separate pieces of the element may be formed at thecentral portion and the bend portion to leave the bend allowance sectionfree of such element. Some components in the central portion and thebend portion can be electrically connected via one or more conductiveline trace 120 laid across the bend allowance section of the flexibledisplay 100.

Instead of being entirely removed from the bend portion, some elementsmay be provided with a bend pattern along the bend lines or otherwisewithin the bend allowance section to reduce the bend stress. FIG. 3illustrates a plane view and a cross-sectional view of exemplary bendpatterns 300. It should be noted that the order of the bend patternsillustrated in the plane view of the flexible display 100 do notnecessarily match with the order of bend patterns illustrated in thecross sectional view of the flexible display 100 in FIG. 3. The bendpatterns 300 described above may be used in the support layer 108, thepolarization layer 110, the touch sensor layer 114 and various otherelements of the flexible display 100.

The flexible display 100 may utilize more than one types of bendpatterns. It should be appreciated that a number of bend patterns andthe types of the bend patterns 300 utilized by the components is notlimited. If desired, the depth of the patterns may not be deep enough topenetrate through the component entirely but penetrate only partiallythrough the respective layer. In addition, a buffer layer positionedbetween the base layer 106 and the TFT as well as a passivation layercovering a conductive line trace may be also be provided with the bendpattern for reducing bend stress.

Several conductive lines are included in the flexible display 100 forelectrical interconnections between various components therein. Thecircuits fabricated in the active area and inactive area may transmitvarious signals via one or more conductive lines to provide a number offunctionalities in the flexible display 100. As briefly discussed, someconductive lines may be used to provide interconnections between thecircuits and/or other components in the central portion and the bendportion of the flexible display 100.

As used herein, the conductive lines broadly refers to a conductive pathfor transmitting any type of electrical signals, power and/or voltagesfrom one point to another point in the flexible display 100. As such,the conductive lines may include source/drain electrodes of the TFTs aswell as the gate lines/data lines used in transmitting signals from someof the display driving circuits (e.g., gate driver, data driver) in theinactive area to the pixel circuits in the active area. Likewise, someconductive lines, such as the touch sensor electrodes, pressure sensorelectrodes and/or fingerprint sensor electrodes may provide signals forsensing touch input or recognizing fingerprints on the flexible display100. The conductive lines can also provide interconnections between thepixels of the active area in the central portion and the pixels of thesecondary active area in the bend portion of the flexible display 100.Aforementioned functionalities of conductive lines in the flexibledisplay 100 are merely illustrative.

Some of the conductive lines may be extended from the substantially flatportion of the flexible display 100 to the bend portion of the flexibledisplay 100. In such cases, some portions of the conductive lines may beconfigured differently from the other portions to withstand the bendingstress. In particular, the portion of the conductive lines laid over thebend allowance section of the flexible display 100 may include severalfeatures for reducing cracks and fractures of the conductive lines tomaintain proper interconnection.

First, some conductive lines of the flexible display 100 may have amulti-layered structure, which may allow more flexibility with lesschance of breakage. FIGS. 4A and 4B each illustrates exemplary stackstructure of the conductive line trace 120.

In FIG. 4A, the conductive line trace 120 may have a multi-layeredstructure in which the primary conductive layer 122 is sandwichedbetween the secondary conductive layers 124. The primary conductivelayer 122 may be formed of material with a lower electrical resistancethan that of the secondary conductive layer 144. Non-limiting examplesof the materials for the primary conductive layer 122 includes copper,aluminum, transparent conductive oxide, or other flexible conductors.The secondary conductive layer 124 should be formed of conductivematerial that can exhibit sufficiently low ohmic contact resistance whenformed in a stack over the primary conductive layer 122.

Examples of such combination include an aluminum layer sandwichedbetween titanium layers (Ti/Al/Ti), an aluminum layer sandwiched betweenupper and lower molybdenum layers (Mo/Al/Mo), a copper layer sandwichedbetween titanium layers (Ti/Co/Ti) and a copper layer sandwiched betweenupper and lower molybdenum layers (Mo/Co/Mo). However, the low ohmiccontact resistance of the conductive layer stack is not the only factorfor choosing the materials for the conductive line trace 120 used in theflexible display 100.

The materials for forming the conductive line trace 120 should meet theminimum Young's modulus requirement while meeting the stringentelectrical and thermal requirements of the flexible display 100 (e.g.,resistance, heat generation, etc.). Accordingly, both the primaryconductive layer 122 and the secondary conductive layer 124 should beformed of materials exhibiting low brittleness (E). In this regard, Alhas a modulus of about 71 GPa, Ti has a modulus of 116 GPa, and Mo has amodulus of 329 GPa. As such, the brittleness (E) of Al is about ¼ ofthat of Mo, and the brittleness (E) of Ti is about ⅓ of that of Mo.Accordingly, in some embodiments, at least some of the conductive lines120 of the flexible display 100 are formed of a stack including Al andTI. Unlike Mo, both Al and Ti exhibited no cracks at the bend radius of0.5 mm.

Since the primary conductive layer 122 should have lower electricalresistance than the secondary conductive layer 124, the conductive linetrace 120 may be formed in a stack of Ti/Al/Ti. In particular, at leastsome of the conductive lines 120 disposed in the bend allowance sectionmay be formed in a stack of Ti/Al/Ti.

In some embodiments, the flexible display 100 may be employed in awearable electronic device. In such cases, the flexible display 100 maybe used under highly humid environment. In some cases, moistures canreach the conductive line trace 120. Dissimilar metals and alloys havedifferent electrode potentials, and when two or more come into contactin an electrolyte, one metal acts as anode and the other as cathode. Theelectro-potential difference between the dissimilar metals is thedriving force for an accelerated attack on the anode member of thegalvanic couple, which is the primary conductive layer 122 in theTi/Al/Ti stack. The anode metal dissolves into the electrolyte, anddeposit collects on the cathodic metal. Due to Al layer corrosion,electrical characteristics of the conductive line trace 120 may bedeteriorated or completely lost.

Typically, galvanic corrosion is initiated by the electrolyte that is incontact at the cross-sectional side of a multi-layered conductive linetrace 120. Accordingly, in some embodiments, at least some conductivelines 120 is provided with a structure in which the primary conductivelayer 122 is surrounded by the secondary conductive layer 124 such thatthe primary conductive layer 122 are covered by the secondary conductivelayer 124 as shown in FIG. 4B. This can minimize the loss of primaryconductive layer 122 by galvanic corrosion, and further reduceprobability of severance of electrical conductivity.

Such a multi-layered conductive lines 120 can be created by firstdepositing the material for the primary conductive layer 122 (e.g., Al)over the secondary conductive layer 124 (e.g., Ti). Here, the secondaryconductive layer 124 underneath the primary conductive layer 122 mayhave greater width. Etch resist material is formed over the stack ofthese two layers and etched (e.g., dry etch, wet etch, etc.) to form adesired a conductive line trace (e.g., diamond trace design). Afterstriping the etch resistance material, another layer of secondaryconductive layer 124 (i.e., Ti) is deposited over the patternedstructure (i.e., Ti/Al). Again, the secondary conductive layer 124 ontop of the primary conductive layer 122 may have greater width such thatthe primary conductive layer 122 is enclosed within the secondaryconductive layer 124. Another round of dry etching and striping of theetch resistance material is performed to form the stack of themulti-layered structure (i.e., Ti/Al/Ti) in a desired conductive linetrace design.

Various insulation layers, such as the a buffer layer 126, thepassivation layer 128, a gate insulation layer (GI layer) and aninterlayer dielectric layer (ILD layer) may be formed at the lowerand/or upper side of the conductive line trace 120. These insulationlayers may be formed of organic and/or inorganic materials or include asub-layer formed of inorganic materials.

A layer of inorganic material is generally less ductile than the metalsof the conductive lines 120. Given the same amount of bending stress,cracks generally initiate from the insulation layers for the conductiveline trace 120. Even if the conductive lines trace 120 has sufficientmodulus to withstand the bending stress without a crack, the cracksinitiated from the insulation layer tend to grow and propagate into theconductive lines 120, creating spots of poor electrical contacts thatcould render the flexible display 100 unusable. Accordingly, variousbending stress reduction techniques are utilized in both the insulationlayers and the conductive lines 120.

It should be noted that cracks primarily propagate through inorganicinsulation layers. Accordingly, propagation of cracks can be suppressedby selectively removing inorganic insulation layers from the areas proneto cracks. Accordingly, the inorganic insulation layers and/or stack ofinsulation layers including a layer of inorganic material can beselectively etched away at certain parts of the flexible display 100.

For example, the insulation layer under the conductive line trace 120can be etched away as depicted in FIG. 5A. The insulation layer underthe conductive line trace 120 may be the buffer layer 126, which mayinclude one or more layers of inorganic material layers. The bufferlayer 126 may be formed of one or more layers of a SiN_(x) layer and aSiO₂ layer. In one suitable configuration, the buffer layer 126 may beformed of alternating stacks of a SiN_(x) layer and a SiO₂ layer. Thebuffer layer 126 is disposed on the base layer 126, but under the TFT.

The buffer layer 126 formed on the substantially flat portion of thebase layer 106 may be thicker than the buffer layer 126 over the bendportion of the base layer 106. To facilitate easier bending of theflexible display 100, a part of the buffer layer 126 may etched away inthe bend portion of the flexible display 100. As such, the buffer layer126 in the substantially flat portion of the flexible display 100 has atleast one additional sub-layer than the buffer layer in the bend portionof the flexible display 100. For example, the buffer layer 126 in thesubstantially flat portion may include multiple stacks of a SiN_(x)layer and a SiO₂ layer, and the buffer layer 126 in the bend portionincludes a single stack of a SiN_(x) layer and a SiO₂ layer. It is alsopossible to have only a single layer of either a SiN_(x) layer or a SiO₂layer in some part of the bend portion.

Each SiN_(x) layer and SiO₂ layer of the stacked buffer 126 may have athickness of about 1000 Å. As such, the thickness of the buffer layer inthe bend portion of the flexible display may range from about 100 Å toabout 2000 Å. In the substantially flat portion of the flexible display100, additional layer of inorganic layer may be provided immediatelybelow the semiconductor layer of the TFT. The inorganic layer that ispositioned closest under the active layer of the TFT may be much thickerthan the individual inorganic layers of the buffer 126.

In the bend allowance section, the buffer layer 126 may be etched evenfurther to expose the base layer 106 while leaving the buffer layer 126intact under the conductive line trace 120. In other words, a recessedarea and a protruded area are provided in the bend portion of theflexible display 100. The protruded area includes the buffer layer 126provided on the base layer 106, whereas the recessed area has the baselayer 106 exposed without the buffer layer 126 disposed thereon.

The conductive line trace 120 is positioned on the protruded area, andthe passivation layer 128 is positioned over the conductive line trace120 on the protruded area. Although the passivation layer 128 may betemporarily deposited over the recessed area, the passivation layer 128can be removed from the recessed area by dry etch or wet etch process.As such, the recessed area can be substantially free of the passivationlayer 128. When etching the passivation layer 128 from the recessedarea, part of the base layer 106 can also be etched. Accordingly, thethickness of the base layer 106 at the recessed area can be lower thanthat of the base layer 106 elsewhere in the flexible display 100. Whenthe buffer layer 126 is etched away as shown in FIG. 5A, the crackpropagation from the buffer 126 to the conductive line trace 120 can bereduced due to the recessed area.

As illustrated in FIG. 5B, in some embodiments, the recessed areaincludes the base layer 106 that is etched to a certain depth, and theconductive line trace 120 is deposited on the base layer 106 of therecessed area. In this setting, the portion of the conductive line trace120 is disposed within the base layer 106. The conductive line trace 120is also deposited on a part of the buffer layer 126 that provides theprotruded area. A passivation layer 128 can be deposited over theconductive line trace 120, and then etched away from the recessed areato expose the conductive line trace 120 in the recessed area.

Accordingly, the passivation layer 128 remains on the conductive linetrace 120 positioned on the protruded area. In this configuration, thepassivation layer 128 remaining on the buffer layer 126 inhibitsgalvanic corrosion as it covers the side surface of the multi-layeredconductive line trace 120. Accordingly, the conductive line trace 120 inthe recessed area needs not be covered by the passivation layer 128. Inthis configuration, cracks generated from the buffer 126 may penetrateto the conductive line trace 120 on the side surface of the buffer layer126, but not the part of the conductive line trace 120 positioned withinthe base layer 106. With the passivation layer 128 removed from thesurface of the conductive line trace 120 in the recessed area, crackpropagation from the passivation layer 128 can also be prevented. Sincegalvanic corrosion starts from the edge of the conductive line trace 120on the buffer layer, the passivation layer 128 covering the edge of theconductive lines 120 on the buffer 126 may not be needed if the distancebetween the conductive line trace 120 on the buffer layer 126 and theconductive line trace 120 in the base layer 106 is sufficiently far.

Crack can also occur in the insulation layers during scribing and/orchamfering some part of the flexible display 100. The cracks generatedat the edge of the flexible display 100 during such manufacturingprocesses can propagate towards central portion of the flexible display100. In some cases, cracks at the edge of the side inactive areaspropagate towards the active area and damage GIPs in the inactive areas.

Accordingly, inorganic layers at the top and bottom edges as to minimizethe crack initiation from the scribing line of the flexible display 100.More specifically, the buffer layer 126 can be etched along the top andbottom edges, in the area denoted as “the scribe line etch area” in FIG.6A. In these areas, the base layer 106 may be exposed or only a minimalthickness of inorganic layer to be remained along the scribe line of theflexible display 100.

Several crack stopper structures may also be provided at the sides ofthe active area. For instance, a recessed channel can be formed in theinactive area by etching the insulation layers as shown on the left sideedge of the active area in FIG. 6A. In some embodiments, a metal andinsulation layer pattern capable of changing the direction of crack canbe formed between a circuit positioned in the inactive area and theouter edge of the inactive area. For example, a metal trace having astrain reduction pattern and insulation layer covering the metal tracecan be formed between the GIP and the edge of the flexible display 100as the right side of the flexible display 100 in FIG. 6A.

It should be noted that the recessed channel on the left side of theactive area can also be provided on the right side of the active area.Likewise, the metal trace with the strain-reducing pattern provided onthe right side of the inactive area can also be provided on the leftside of the inactive area. In some embodiments, both the recessedchannel and the metal trace having the strain-reducing pattern can beprovided on both sides of the active area. In this configuration, thecracks propagating from the outer edge of the inactive area in thedirection towards the GIP may change its course due to the angle of thediamond metal/insulation trace formed before the GIP.

Etching of the insulation layers can also be performed in the routingarea between the active area and the bend allowance section as well asthe routing area between the COF area and the bend allowance section.Further, the inorganic layers may be removed from the areas next to thechamfering lines so that cracks do not propagate from the chamferingline side towards the conductive lines 120.

FIG. 6B is an enlarged view of the bend allowance section near thechamfering line. In order to reduce crack initiation and propagationfrom the inorganic layers near the chamfering line, the insulation layeris etched away in the area from the VSS line to the chamfering line isetched. In particular, the buffer layer 126 disposed in the area betweenthe closest conductive lines 120 in the bend allowance section (e.g.,VSS) and the chamfering line can be etched away. In this area, the baselayer 106 (e.g., PI) may be exposed or only minimal amount of bufferlayer 126 may be left. Accordingly, crack initiation and propagationfrom the chamfering line can be minimized.

When etching the buffer layer 126 near the chamfering line, a stripe ofbuffer layer 126 may be left between the chamfering line and the closestconductive line trace 120 (e.g., VSS). Such a stripe of buffer layer canserve as a dam for inhibiting moistures of other foreign material fromreaching the conductive line trace 120 from the chamfered side of theflexible display 100.

The removal of the buffer layer 126 can also be applied in the routingarea between the chamfering line and the closest conductive line 120.The stripe of buffer layer 126 may also be provided in the routing area.Further, the buffer layer 126 under the conductive lines 120 and thepassivation layer 128 on the conductive lines 120 can be etched awaythroughout the routing area to further reduce the chance of crackpropagation by the inorganic layers in the routing area. Accordingly,the structure depicted in FIGS. 5A and 5B may also be applied to theconductive line traces 120 in the routing area.

FIG. 6C is an enlarged view of the bend allowance section near thechamfering line provided with another crack stopper structure. In thisembodiment, an auxiliary conductive line 130 having the diamond tracepattern is provided between the chamfering line and the conductive linetrace 120 (e.g., VSS). The buffer layer 126 under the auxiliaryconductive line 130 and the passivation 128 on the auxiliary conductiveline 130 can be etched in the similar manner as depicted in FIGS. 5A and5B. Accordingly, the auxiliary conductive line 130 may inhibitpropagation of cracks from the chamfering line to the conductive linetrace 130. The auxiliary conductive line 130 may be a floating line. Ifdesired, the auxiliary conductive line 130 may extend further towardsbottom edge of the flexible display 100. In some embodiments, theauxiliary conductive line 130 may be in contact with adjacent conductiveline 120. In addition to the auxiliary conductive line 130, the stripeof buffer layer 126 may also be provided to stop moisture or otherforeign materials traveling towards the auxiliary conductive line 130.

Removal of inorganic insulation layers near the TFTs of the flexibledisplay 100 may affect the electrical characteristic of components inthe flexible display 100. For instance, undesired shift in the thresholdvoltage of TFTs was observed when SiN_(x) layers were removed from thebuffer layer 126. In order to maintain the stability of the TFTs, anadditional shield metal layer can be formed under the semiconductorlayer of the TFTs. The shield metal layer may be under the buffer layer126 or interposed between the inorganic layers of the buffer layer 126.In some embodiments, the shield metal layer may be electricallyconnected to the source electrode or gate electrode of the TFTs.

A trace designs plays an important role in reducing the bending stressin both the conductive line trace 120 and the insulation layers. Forconvenience of explanation, the conductive line trace 120 and the traceof insulation layer (i.e., passivation layer 128) covering at least somepart of the conductive line trace 120 are collectively referred to asthe “wire trace” in the following description.

The trace design should be determined by considering the electricalrequirements of the conductive line trace 120 as well as the type ofsignals transmitted on the conductive line trace 120. Also, theproperties of the materials (e.g., Young's modulus) used in forming theconductive line trace 120 and the insulation layers can be considered indesigning the traces. It should be noted that various other factors suchas a thickness, a width, a length, a layout angle for a section as wellas for the entirety of the conductive line trace 120 and the insulationlayers may need to be considered to provide a trace design havingsufficient electrical and mechanical reliability for use in the flexibledisplay 100.

The wire trace design may be specifically tailored for the conductiveline trace 120 and the insulation layers based on their placement andorientation in reference to the bending direction (i.e., tangent vectorof the curve) of the flexible display 100. A wire trace will besubjected to more bending stress as the direction in which the wiretrace extends is more aligned to the tangent vector of the curvature. Inother words, a wire trace will withstand better against the bendingstress when the length of the wire trace aligned to the tangent vectorof the curvature is reduced.

In order to reduce the length of the wire trace portion being aligned tothe tangent vector of the curvature, wire traces of the flexible display100 may employ any one or more of a sign-wave, a square-wave, aserpentine, a saw-toothed and a slanted line trace designs illustratedin FIG. 7. In such configurations, the bending stress may be distributedto the trace portions oriented in an angle shifted away from the tangentvector of the curvature. The strain-reducing trace designs illustratedin FIG. 7 are merely exemplary and should not be construed aslimitations to the trace designs that can be used in the embodiments ofthe flexible display 100.

Some conductive line trace 120 may adopt different strain-reducing tracedesigns from other conductive line trace 120 of the flexible display100. In some embodiments, the conductive line trace 120 can have varyingdimensions to facilitate tight spacing between the conductive lines. Forinstance, a convex side of a first wire trace may be placed in a concaveside of a second wire trace next to the first wire trace.

In order to prevent or minimize severance of interconnections by cracksin the conductive line trace 120, the wire trace may split into multiplesub-traces, which and converge back into a single trace at a certaininterval. In the example of FIG. 8A, a single trace of a conductive linetrace 120 includes sub-trace A and sub-trace B, which merge back atevery joint X, resembling a chain of diamonds. This trace design may bereferred hereinafter as the diamond trace design. Because sub-traces arearranged to extend in the vector angled away from the tangent vector ofthe curvature, reduction in the length of the wire trace being alignedwith the tangent vector of the curvature was realized in the similarmanner as the trace designs illustrated in FIG. 7.

The diamond trace design shown in FIG. 8 provides a significantelectrical advantage over the single line wire trace designs of the FIG.7. First, given the same width, thickness and the angle shifting awayfrom the tangent vector of the curve, nearly the half of electricalresistance was observed from the wire trace employing the diamond tracedesign in comparison to the wire trace employing the mountain tracedesign (i.e., 4.4Ω:8.6Ω). In addition, splitting of the trace intomultiple sub-traces may provide a backup electrical pathway in case oneof the sub-traces is damaged by cracks. As such, the diamond tracedesign can be used for the wire traces in the bend portion, and may beparticularly helpful for the wire traces within the bend allowancesection subjected to severe bending stress.

As mentioned, the distribution of the bending stress depends on thevector (i.e., split angle) of the sub-traces in reference to the bendingdirection. The sub-trace having a larger split angle away from thebending direction (i.e., tangent vector of the curvature) will besubjected to less bending stress. However, it should be noted that thesplit of the wire trace into multiple sub-traces do not by itselfprovide bend stress reduction on each sub-trace any more than the bendstress reduction realized by the orientation of the wire trace beingangled away from the tangent vector of the curvature. In fact, given thesame conductive line width and angle of deviation from the tangentvector of the curvature, the result of bend stress simulation in amountain shaped wire trace, which almost mirrors the shape of the one ofthe sub-traces in the diamond trace design, was nearly identical to theresult of bend stress simulation exhibited on each sub-trace of thediamond trace design.

However, one of the extra benefits realized from the diamond tracedesign is that the design allows to minimize or to eliminate the lengthof insulation layer trace being aligned (i.e., running parallel) to thetangent vector of the curvature with relatively little increase in theelectrical resistance. Since the cracks generally initiate from theinsulation layer, it is imperative that the length of the insulationtrace being aligned with the tangent vector of the curvature isminimized. When using the diamond trace design, an offset is createdbetween the locations of the conductive line trace 120 at the stresspoint A and the conductive line trace 120 at the stress point B, hencereduces the length of the conductive line trace 120 being aligned to thetangent vector of the curvature.

The same applies to the buffer layer 126 under the conductive line trace120 as well as the passivation layer 128 on the conductive line trace120. In other words, the inorganic buffer layer 126 is etched away inthe area between buffer layer 126 at the stress point A and the stresspoint B such no continuous straight-line path of buffer layer 126 existsbetween two points. Likewise, the passivation layer 128 is etched awayin the area between passivation layer 128 at the stress point A and thestress point B such no continuous straight-line path of passivationlayer 128 exists between two points. Not only does the diamond tracedesign provide much lower crack initiation rate, but it also hinders thepropagation of cracks to the conductive line trace 120.

Reduction of the insulation layer trace aligned to the tangent vector ofthe curvature can be done by reducing the width of the conductive linetrace 120 and the insulation layer covering the conductive line trace120. When the insulation layer trace aligned to the tangent vector ofthe curve is eliminated by reduction of conductive line width and theinsulation trace width, the average size of cracks was reduced from 3.79μm to 2.69 μm. The ohmic contact resistance was increased to 4.51Ω from3.15Ω, but such an increase has minimal effect in the operation of theflexible display 100.

The amount of reduction in the width of conductive line trace 120 islimited with the single line trace designs depicted in FIG. 7 as theelectrical resistance of the conductive line trace 120 can become toohigh to be used for the flexible display 100. However, the additionalelectrical pathway created by splitting and merging of the conductiveline trace 120 yields much lower electrical resistance in the conductiveline trace 120 as compared to using the non-split strain-reducing tracedesigns.

It should be noted that the splitting angle of the sub-traces affectsthe distance between the two adjacent joints X in the diamond tracedesign 800. The distance between the joints X need not be uniformthroughout the entire wire trace. The intervals at which the tracesplits and merges can vary within a single trace of wire based on thelevel of bending stress exerted on the parts of the wire trace. Thedistance between the joints X may be progressively shortened down forthe parts of the wire trace towards the area of the flexible display 100subjected to higher bending stress (e.g., area having lower radius ofcurvature, area having larger bend angle). Conversely, the distancesbetween the joints X can progressively widen out towards the areasubjected to lower bending stress.

In an exemplary trace design of FIG. 8B, the distance between the jointsX of a trace in the end sections is at a first distance (e.g., 27 um),but the distance becomes progressively shorter towards the mid-sectionof the trace. In the mid-section, the distance between the joints X isreduced by half. The end sections of the trace shown in FIG. 8B may befor the part of the wire trace near the beginning of a bend allowancesection, and the mid-section of the trace may be for the part positionedat or near the middle of the bend allowance section of the flexibledisplay 100.

A lower chance of crack initiation is afforded in the wire trace byselectively increasing the angle of sub-traces in the wire trace at highbending stress regions. With sub-traces that split and merge at agreater angle away from the bending direction, more thorough reductionin the lengths of the conductive line trace 120 and the insulation layerextending along the tangent vector of the curvature. This way,unnecessary increase in the electrical resistance can be avoided.

The wire trace may split into additional number of sub-traces, creatinga grid-like wire trace in the bending area of the flexible display 100as illustrated in FIG. 8C. As an example, the sub-traces can beconfigured to form a plurality of a web formed of diamond trace shapes.Such trace design may be useful for wire traces that transmit a commonsignal, for example VSS and VDD. Neither the number of sub-traces northe shapes of the sub-traces forming the grid-like trace design areparticularly limited as the example shown in FIG. 8C. In someembodiments, the sub-traces may converge into a single trace past thebend allowance section of the flexible display 100.

The strain-reducing trace designs discussed above may be used for all orparts of the conductive line trace 120. In some embodiments, the part ofconductive line trace 120 in the bend portion of the flexible display100 may adopt such a strain-reducing trace design. The parts of aconductive line trace 120 prior to or beyond the part with thestrain-reducing trace design may have the same trace design. If desired,the strain-reducing trace designs may be applied to multiple parts of aconductive line trace 120.

Even with the strain-reducing trace design, the inevitable bendingstress remains at certain points of the trace (i.e., stress point). Thelocation of stress point is largely dependent on the shape of the traceas well as the bending direction. It follows that, for a given bendingdirection, the trace of a wire and/or an insulation layer can bedesigned such that the remaining bending stress would concentrate at thedesired parts of their trace. Accordingly, a crack resistance area canbe provided in a trace design to reinforce the part of the wire tracewhere the bend stress concentrates.

Referring back to FIG. 8A, when a wire trace having the diamond tracedesign is bent in the bending direction, the bending stress tends tofocus at the angled corners, which are denoted as the stress point A andstress point B. When a crack forms at those angled corners, it generallygrows in the transverse direction that to the bending direction. Forinstance, at the stress points A, a crack may initiate from the outertrace line 820 and grows towards the inner trace line 830. Similarly, acrack may initiate from the outer trace line 830 and grow towards theinner trace line 820 at the stress points B.

Accordingly, the width of the conductive line trace 120 at the stresspoints A can be selectively increase in transversal direction to thebending direction, thereby serving as a crack resistance area. That is,the widths (W_(A), W_(B)) of the conductive line trace 120 at the stresspoints A and B, which are measured in the crack growth direction, may belonger than the width (W) of the conductive line trace 120 at otherparts as depicted in FIG. 8A. The extra width in the crack growthdirection at the stress points makes the conductive line trace 120 tohold out longer before a complete disconnection occurs.

In a testing, the wires had the three-layered structure (MO 200 Å/AL3000 Å/MO 200 Å), which were formed on a 17 um thick PI base layer 106.A 1000 Å thick SiN_(x) layer was formed between the base layer 106 andthe multi-layered conductive line trace 120. Also, a layer of SiO₂ wasformed over the multi-layered conductive line trace 120. The thickestportion of the SiO₂ on the conductive line trace 120 was 3000 Å. Each ofthe conductive lines 1 through 4 had different width a width of 8.5 um,2.5 um, 3.5 um and 4.5 um, respectively, at the stress points A.

For each wire trace, electrical resistance was measured initially uponthe bending and again at 15 hours later. If a crack is generated in theconductive line trace 120, the resistance of the conductive line trace120 will be increased as well. The wire trace 1 with the longest widthat the stress points A exhibited the lowest mean increase resistancerate whereas the wire 2 with the shortest width at the stress points Aexhibited the largest mean increase resistance rate. Also, a completeseverance was observed in three samples of the wire trace 2 and twosamples of the wire trace 3. While complete severance in the wire trace4, a considerable increase in the resistance was observed after 15hours. Accordingly, a sufficient width at the stress points A is neededto maintain the reliability of the wire.

For instance, the width of the wire at the stress points A may be longerthan 4.0 um. The width of the wire measured in the direction of thecrack growth direction may be longer than 5.0 um for further improvementin the reliability. Even with the increased width of the conductive linetrace 120 in the transversal direction to the bending direction, thelength for the continuous portion of the insulation layer being alignedto the bending direction should be kept minimal. Accordingly, in anembodiment, the width of the wire at the stress points A ranges fromabout 2.5 um to about 8 um, more preferably, from about 3.5 um to about6 um, more preferably from about 4.5 um to about 8.5 um, and morepreferably at about 4.0 um.

The width of the conductive line trace 120 measured in the crack growthdirection at the stress points B should also be maintained in thesimilar manner as the width of the conductive line trace 120 at thestress points A. As such, the width of the wire at the stress points Bmay ranges from about 2.5 um to about 8 um, more preferably, from about3.5 um to about 6 um, more preferably from about 4.5 um to about 8.5 um,and more preferably at about 4.0 um. Due to the close proximity of theangled corners and their crack growth direction at the stress points B,the width of the conductive line trace 120 at the stress points B may belonger than width at the stress points A.

In order to minimize the chance of crack initiating from both the innertrace line 820 and the outer trace line 830, at least one of the tracelines may not be as sharply angled as the other trace lines at thestress points A. In the embodiment depicted in FIG. 8A, the inner traceline 820 at the stress points A has the angled corner and the outertrace line 830 at the stress points A is substantially parallel (e.g.,±5°) to the bending direction. However, the length L of the outer traceline 830 extending in the bending direction in excess may defeat thepurpose of utilizing the strain-reducing trace design in the firstplace. As such, the length L for the portion of the outer trace line 830extending substantially parallel to the bending direction may be equalto or deviate slightly (e.g., within ±2.5 μm) from the width W of thewire trace. Alternatively, the sharply angled corner can be formed withthe outer trace line 830 while the inner trace line 820 at the stresspoints A being substantially parallel to the bending direction. In bothcases, the less sharply angled trace line can simply be more roundedrather than having the straight line trace as shown in FIG. 8A.

As discussed above, splitting and merging of the wire creates stresspoints that share the given amount of bending stress. With therelatively low bending stress at each stress point, there is less chanceof crack initiation. In some cases, however, available space on theflexible display 100 may limit the number of joints X of a trace. Thatis, excess joints X in a wire trace may take up too much space in theflexible display 100. On the other hand, the limited number of joints Xin a trace may not be enough to prevent or minimize crack initiating atthe stress points.

Accordingly, a trace may be provided with a number of micro-stresspoints 810 that are strategically positioned along one or moresub-traces such that the bending stress on the sub-trace is distributedamong the micro-stress points 810. In the example depicted in FIG. 8D,the insulation trace includes a number of micro-stress points 810. Asdiscussed, the angled corners tend to be the stress points in a tracedesign. Thus a plurality of angled cutouts can be formed along theinsulation layer trace to serve as a micro stress points 810. In thissetting, at least some fraction of the bending stress on each of thesub-traces would be focused on each of the micro-stress points 810. Witheach micro-stress points 810 taking up the fraction of the given bendingstress on the sub-traces, the size of the crack at each micro-stresspoints 810 may be smaller than a crack size that would result in theinsulation layer trace without the micro-stress points 810. Accordingly,this can reduce the chance of complete severance of the conductive linetrace 120.

It should be appreciated that the location and the number ofmicro-stress points 810 is not limited as shown in FIG. 8D. Additionalmicro-stress points 810 can be formed at the desired location in therespective insulation traces to further reduce the chance of crackinitiation.

As discussed above, some structural elements may not exist in some areasof the flexible display 100 to facilitate bending. For example, elementssuch as the touch sensor layer 112, polarization layer 110 and the likemay be absent in the bend area of the flexible display 100. Also, someof the insulation layers, for instance the buffer layer 126, may beetched in some degree so that the insulation layer has less number ofsub-layers or has a decreased thickness at one area as compared to otherareas in the flexible display 100. Absence or simplification of thesecomponents and the layers would create a recessed area where the wiretrace and/or the insulation layer trace need to cross.

The amount of bending stress and the direction in which the bendingstress is exerted on the wire trace laid over the recessed area maydiffer from the bending stress exerted to other parts of bend portion.To accommodate the difference, the strain-reducing trace design for thewire traces at the recessed area can also differ from thestrain-reducing trace design used elsewhere.

FIG. 9A illustrates a cross-sectional view at an edge of a backplane ofthe exemplary flexible display 100, in which several insulation layersare removed from the bend portion to facilitate more reliable bending.

As shown, there are several organic and inorganic layers formed inbetween the base layer 106 and the OLED element layer 102. In thisparticular example, alternating stacks of SiN_(x) and SiO₂ layers can bedisposed on the base layer 106 to serve as the buffer layer 126. Thesemiconductor layer of a TFT may be sandwiched by an active-buffer layerand a gate insulation layer that are formed of SiO₂ layer. The gate ofthe TFT is disposed on an interlayer dielectric layer (ILD), and thesource/drain of the TFT having the multi-layered structure as discussedabove is sandwiched between the ILD and a passivation layer. Here, theILD may be formed of a stack of SiN_(x) and SiO₂, and the passivationlayer is formed of SiN_(x). Then, a planarization layer is disposed overthe passivation layer so that the anode for the OLED can be disposedthereon.

As mentioned above, use of the strain-reducing trace design is not justlimited to the part of the wire traces within the bend portion. In otherwords, the strain-reducing trace design can be applied to the part ofthe wire traces in the routing areas outside the bend allowance section.Using the strain-reducing trace design for the wire trace in suchrouting area can afford increased protection to the wire trace againstthe bending stress.

In the routing area, however, several layers between the base layer 106and the OLED element layer 102 are absent to facilitate bending of theflexible display 100. For instance, the ILD and the gate insulationlayer is etched away in the trimmed area by the first etch process,which is followed by the second etch process that etches away the activebuffer and a part of the buffer 126 (e.g., a stack of a SiN_(x) layerand a SiO₂ layer). These etching processes create multiple steps where asharp change of direction occurs between the wire trace disposed on thevertically sloped surfaces and the wire trace disposed on thehorizontally leveled surfaces. In other words, the wire trace would haveseveral bent spots, such as EB1 and EB2.

When bending the flexible display 100 in the bending direction, the wiretrace may experience more strain at or near the steps. Numerous testsand experiments indicate that the chance of a crack is especially highin the wire trace crossing over the step between the EB1 area and theEB2 area. Accordingly, in some embodiments, the strain-reducing tracedesign for the wire trace has a reinforced portion at or near the stepbetween a high-leveled surface and a low-leveled surface provided byinsulation layers of the flexible display.

In the example shown in FIG. 9B, the wire trace has a simple straightline trace design in the beginning, which is changed into the split andmerge strain-reducing trace design in the abridged area. In addition,the part of the conductive line that crosses over before and after thebent spots EB1 and EB2 is reinforced with extra width W_(R). That is,the conductive line has substantially wider width to reinforce theconductive line trace 120 near the bent spots EB1 and EB2 to ensure thepreservation of the conductive line trace 120 even if cracks initiatefrom the insulation layer covering the reinforced portion of theconductive line. The distance D_(R) of the reinforced portion of whichthe conductive line is reinforced with the wider increased width W_(R)depends on the size of the steps created by the etching processes aswell as the distance between the bent spots EB1 and EB2. Past thereinforced part, the wire trace continues with the diamond chain-liketrace design discussed above. The strain-reducing trace design for thewire trace that comes before and after the reinforced portion is notparticularly limited to the trace design as depicted in FIG. 9B, and anyother strain-reducing trace design discussed above may be used.

While this may not always be the case, the routing areas adjacent to thebend allowance section may be the substantially flat parts of theflexible display 100. In such cases, the bent spots EB1 and EB2 would bepositioned at or just outside start of the bend allowance section in thebend portion.

The increased width W_(R) of the reinforced conductive line trace 120portion may serve its purpose well at or near the edges of the bendallowance section where the curvature is relatively small. However, thewider width W_(R) of the wire trace would increase the length of thewire trace that is linear to the bending direction. This would be makethe wire trace harder to hold out against the bending stress at theregion with greater bend radius. For this reason, the distance D_(R) inwhich the reinforced portion is used should be limited such that thereinforced conductive line portion does not extend too far beyondtowards into the bend allowance section. In other words, the distanceD_(R) of the reinforced conductive line portion may be limited such thatthe trace design of the reinforced conductive line portion does notextend beyond the bend allowance section with more than a threshold bendangle. In way of an example, the reinforced conductive line portion maynot extend beyond the point where it is 30° curved away from the tangentplane of the curvature. The threshold bend angle may be less than 20°,for example 10°, and more preferably less than 7°.

The wire trace having the reinforced section may extend beyond the bendallowance area routed to pads for COF or other components of theflexible display 100. In such instances, there may be additional bentspots (similar to EB1 and EB2) at or near the end of the bend allowancesection. The conductive line at or near such bent spots may bereinforced in the similar manner as the wire trace portion at the bentspots EB1 and EB2. If desired, the reinforced conductive line portion ator near the bent spots at the other end of the bend allowance sectionmay be different as depicted in FIG. 9B.

With the inorganic insulation layers etched away from the bend portionof the flexible display 100, the wire traces in the bend portion can bevulnerable to moistures and other foreign materials. In particular,various pads and conductive lines for testing the components duringmanufacturing of the flexible display 100 may be chamfered, and this canleave conductive lines exiting at the notched edge of the flexibledisplay 100. Such conductive lines can easily corrode by the moistures,and cause other nearby conductive line traces to corrode as well.

Accordingly, a protective layer, which may be referred to as a“micro-coating layer,” can be provided over the wire traces in the bendportion to provide added protection against moistures and other foreignmaterials. In addition to having a good moisture resistance, themicro-coating layer should have sufficient flexibility so that it can beused in the bend portion of the flexible display 100. Further, thematerial of the micro-coating layer should be curable with low energywithin a limited time so that the components under the micro-coatinglayer are not damaged during the curing process.

FIG. 10A is a schematic illustration of one suitable exemplaryconfiguration of the micro-coating layer 132 in an embodiment offlexible display 100. The micro-coating layer 132 may be provided asphoto-curable (e.g., UV light, Visible light, UV LED) resin and coatedover the desired areas of the flexible display 100. In this regard, themicro-coating layer 132 is coated over the area between theencapsulation 114 and the COF 134 attached in the inactive area.Depending on the adhesive property of the micro-coating layer 132,however, the micro-coating layer 132 can be detached from theencapsulation 114 and/or the COF 134. Any open space between themicro-coating layer 132 and the encapsulation 114 or the COF 132 maybecome a defect site where moisture can permeate through.

Accordingly, the micro-coating layer 132 may be coated to overflow intoa part of the top surface of the encapsulation 114 for enhanced sealingbetween the encapsulation 114 and the micro-coating layer 132. Theadditional contact area between the micro-coating layer 132 and thesurface of the encapsulation 114 can provide stronger bonding betweenthe two, and reduce the cracks and corrosion of the wire traces at thebend portion of the flexible display 100. Likewise, the micro-coatinglayer 132 can be coated on as least some part of the COF 134 forstronger bonding between the micro-coating layer 132 and the COF 134.

Referring to FIGS. 10B and 10C, the width of the encapsulation 114coated with the micro-coating layer 134 (denoted as Overflow_W1) and thewidth of the COF 134 coated with the micro-coating layer 134 (denoted asOverflow_W2) are not particularly limited and may vary depending on theadhesiveness of the micro-coating layer 132. As shown in FIG. 10B, theflexible display 100 may include a portion where the micro-coating layer132 on the encapsulation 114 is spaced apart from the sidewall of thepolarization layer 110. In some embodiments, the flexible display 100may include a portion where the micro-coating layer 132 on theencapsulation 114 is in contact with the polarization layer 110 disposedon the encapsulation 114 as depicted in FIG. 10C. In one suitableconfiguration, the micro-coating layer 132 may be in contact with thepolarization layer 110 at the two opposite corners (denoted “POL_CT”)while the micro-coating layer 132 only covers up to some part of theencapsulation 114 in the areas between the two opposite corners. Afterthe bending process, the part of the flexible display 100 where themicro-coating layer 132 is spaced apart from the polarization layer 110may be configured as shown in FIG. 11A. In the region wheremicro-coating layer 132 is configured to be in contact with thepolarization layer 110, the flexible display 100 may be configured asshown in FIG. 11B.

It should be noted that the micro-coating layer 132 is dispensed in aresinous form, and may spread on the dispensed surface. The spreadingdynamic depends on the viscosity of the micro-coating layer 132 as wellas the surface energy of which the micro-coating layer 132 is dispensed.As such, the micro-coating layer 132 overflowed into the encapsulation114 may reach the polarization layer 110. When the micro-coating layer132 reaches the sidewall of the polarization layer 114, themicro-coating layer 132 may climb over the sidewall of the polarizationlayer 110. Such sidewall wetting of the micro-coating layer 132 can makeuneven edges over the surface of the polarization layer 132, which maycause various issues when placing another layer thereon. Accordingly,the amount of the micro-coating layer 134 dispensed on the targetedsurface can be adjusted to control the width of the micro-coating layer134 on the encapsulation layer 114.

The micro-coating layer 132 may be coated in a predetermined thicknessto adjust the neutral plane of the flexible display 100 at the bendportion. More specifically, added thickness at the bend portion of theflexible display 100 by the micro-coating layer 132 can change theneutral plane so that the plane of the wire traces is shifted closer tothe neutral plane.

In some embodiments, the thickness of the micro-coating layer 132 in thearea between the encapsulation 114 and the COF 134, which is measuredfrom the surface of the base layer 106, may be substantially the same asthe distance between the surface of the base layer 106 to the topsurface of the encapsulation 104. In such embodiments, the verticaldistance between the top surface of the micro-coating layer 132 in thebend allowance section and the top surface of the encapsulation 114 maybe less than 25 um.

Various resin dispensing methods, such as slit coating, jetting and thelike, may be used to dispense the micro-coating layer 132 at thetargeted surface. In way of an example, the micro-coating layer 132 canbe dispensed by using a jetting valve. The dispensing speed from thejetting valve(s) may be adjusted during the coating process for accuratecontrol of the thickness and the spread size of the micro-coating layer132 at the targeted surface. Further, additional number of jettingvalues may be used to reduce the dispense time and limit the amount ofspread before the micro-coating layer 132 is cured through UVirradiation.

Although the concepts and teachings in the present disclosure aredescribed above with reference to OLED display technology, it should beunderstood that several features may be extensible to any form offlexible display technology, such as electrophoretic, liquid crystal,electrochromic, displays comprising discreet inorganic LED emitters onflexible substrates, electrofluidic, and electrokinetic displays, aswell as any other suitable form of display technology.

As described above, a flexible display 100 may include a plurality ofinnovations configured to allow bending of a portion or portions toreduce apparent border size and/or utilize the side surface of anassembled flexible display 100. In some embodiments, bending may beperformed only in the bend portion and/or the bend allowance sectionhaving only the conductive line trace 120 rather than active displaycomponents or peripheral circuits. In some embodiments, the base layer106 and/or other layers and substrates to be bent may be heated topromote bending without breakage, then cooled after the bending. In someembodiments, metals such as stainless steel with a passive dielectriclayer may be used as the base layer 106 rather than the polymermaterials discussed above. Optical markers may be used in severalidentification and aligning process steps to ensure appropriate bendsabsent breakage of sensitive components. Components of the flexibledisplay 100 may be actively monitored during device assembly and bendingoperations to monitor damage to components and interconnections.

Constituent materials of conductive line trace 120 and/or insulationlayers may be optimized to promote stretching and/or compressing ratherthan breaking within a bending area. Thickness of a conductive linetrace 120 may be varied across a bending area and/or the bend allowancesection to minimize stresses about the bend portion or the bendallowance section of the flexible display 100. Trace design ofconductive line trace 120 and insulation layers may be angled away fromthe bending direction (i.e., tangent vector of the curvature),meandering, waving, or otherwise arranged to reduce possibility ofseverance during bending. The thickness of the conductive line trace120, insulation layers and other components may be altered or optimizedin the bend portion of the flexible display 100 to reduce breakageduring bending. Bend stresses may be reduced by adding protectivemicro-coating layer(s) over components in addition to disclosedencapsulation layers. Conductive films may be applied to the conductiveline trace 120 before, during, or after bending in a repair process.Furthermore, the constituent material and/or the structure forconductive line trace 120 in a substantially flat area of a flexibledisplay 100 may differ from the conductive line trace 120 in a bendportion and/or the bend allowance section.

These various aspects, embodiments, implementations or features of thedescribed embodiments can be used separately or in any combination. Theforegoing is merely illustrative of the principles of this invention andvarious modifications can be made by those skilled in the art withoutdeparting from the scope of the invention.

What is claimed is:
 1. A display apparatus, comprising: a base layerhaving a bend allowance section between a first portion and a secondportion of the display apparatus; a plurality of organic light-emittingdiode (OLED) elements disposed on the first portion of the base layer;an encapsulation over the OLED elements; a printed circuit film attachedto the second portion of the base layer; and a micro-coating layerdisposed over the bend allowance section of the base layer.
 2. Thedisplay apparatus of claim 1, further comprising a plurality of wiretraces routed between the first portion and the second portion of thebase layer, wherein the micro-coating layer is arranged to cover theplurality of wire traces in the bend allowance section.
 3. The displayapparatus of claim 2, wherein the micro-coating layer is arranged tocover a part of the encapsulation.
 4. The display apparatus of claim 3,further comprising a polarization layer on the encapsulation positionedto expose at least some part of an upper surface of the encapsulation,wherein the micro-coating layer is arranged to cover at least part ofthe upper surface of the encapsulation between an edge of polarizationlayer and an edge of the encapsulation.
 5. The display apparatus ofclaim 4, wherein the micro-coating layer covering the upper surface ofthe encapsulation is in contact with the sidewall of the polarizationlayer.
 6. The display apparatus of claim 4, wherein the micro-coatinglayer covering the upper surface of the encapsulation includes a portionthat is in contact with the sidewall of the polarization layer and aportion that is spaced apart from the side wall of the polarizationlayer.
 7. The display apparatus of claim 4, wherein the micro-coatinglayer is arranged to cover a part of the printed circuit film attachedon the second portion of the display apparatus.
 8. The display apparatusof claim 4, further comprising: a buffer layer under the plurality ofwire traces routed between the first portion and the second portion ofthe display apparatus; and a passivation layer on the plurality of wiretraces routed between the first portion and the second portion of thedisplay apparatus, wherein the plurality of wire traces has astrain-reducing trace design in the bend allowance section, and whereinthe buffer layer and the passivation layer in the bend allowance sectionhas a pattern corresponding to the strain-reducing trace design of thewire traces in the bend allowance section.
 9. The display apparatus ofclaim 4, wherein each of the first portion, the second portion and thebend allowance section includes a buffer layer etched area between anotched line and a closest conductive line trace to the notched line.10. The display apparatus of claim 4, further comprising a first supportfilm attached on an inner surface of the first portion of the base layerand a second support film attached on an inner surface of the secondportion of the base layer, wherein the first support film and theencapsulation film are arranged such that the first support film isextended further out toward the bend portion of the base layer than theencapsulation film.
 11. The display apparatus of claim 4, wherein themicro-coating layer is formed of a photo-curable material.
 12. Thedisplay apparatus of claim 4, wherein the micro-coating layer has athicker profile in a first routing area between the encapsulation andthe bend allowance section than a second routing area between theprinted circuit film and the bend allowance section.
 13. The displayapparatus of claim 4, wherein a width of the upper surface of theencapsulation that is covered by the micro-coating layer is greater thana width of the printed circuit film that is covered by the micro-coatinglayer.
 14. The display apparatus of claim 4, wherein a height of themicro-coating layer on the upper surface of the encapsulation is lesserthan a height the micro-coating layer on the printed circuit film.